Production of mold parts



D. E. CUTLER Filed March 15, 1946 PRODUCTION oF MoLD PARTS Aug. w, 1947.

M, v/a...

` 0 ATTORNEYS.

Patented Aug.. 19, 1947 FICE r PRODUCTION F MOLD PARTS Day E. Cutler, Pittsburgh, Pa., Iassignor to The J. S. McCormick Co., Pittsburgh, Pa., a corporation of Pennsylvania Application March 15, 1946, Serial No. 654,715

This invention relates to mold parts made from sand bonded wholly or partially with oil, which for brevity will be referred to herein as oil bonded sand mold parts.

In the production of cast metal articles a standard practice for a great many years has been to use molds provided with baked cores shaped from suitable foundry, or molding,'sand mixed with oil, with or without the addition of supplementary core binder material. A wide variety of oils have been used for this purpose that are` known to and available in the art, typical examples being linseed and soybean oils, although other drying or semi-drying vegetable, mineral and fish oils are likewise used. The supplementary core binders generally are materials used to confer or increase the green or dry bond strength such as rosin, resins, sulfite liquor, dextrinized grain iiours,

gelatinized grain flours, and clays.

Such cores are baked to render them strong enough for use. With the batches used prior to my invention baking cycles of many hours duration have been necessary due to the fact that the oxidation of the oil that is necessary to develop the strength and color that core makers and founders consider desirable occurs relatively slowly wlthin the interior Aof the shaped cores. So far as I am aware, all prior attempts to reduce the baking time while maintaining adequate strength have been unsuccessful. l

Molds themselves may be formed similarly from oil bonded sands. Accordingly, it is to be understood that the term mold parts as used herein contemplates both molds and cores.

A primary object of the present invention is to provide a method of making baked sand mold parts bonded, at least in part, with oil which reduces the time of baking in comparison with Y prior practice, is simple and inexpensive, and

which does not interfere with or involve objectionable modification of existing practices.

A special object is to provide a method in accordance with the preceding object that is productive of mold parts of increased strength.

Still another object is to provide a method of making oil bonded sand mold parts that results in more uniform baking through the section than out their section.

The invention will be described in connection with the accompanying drawing which is a graph Claims. (Cl. 22-188) representative of the results attainable through the practice of the invention.

The invention is predicated upon my d iscovcry that its stated objects are attained by incorporating ammonium nitrate (NHiNOs) in green sand mold parts bonded at least in part with oil, and then baking the parts. Specifically, I have found that when foundry sand and oil in accordance withordinary sand mold practice involving the use of oil as a binder are mixed thoroughly with ammonium nitrate in certain definite proportions, and mold parts are shaped from the mixture and then baked, the baked parts attain adequate tensile strength, and develop the color that is believed to indicate complete baking, in much less time than is necessary for the same parts without ammonium nitrate and baked under the same conditions. Likewise, in most instances parts made in accordance with the invention possess substantially greater strength, not only after less than normal baking times, but after baking during the time intervals necessary when ammonium nitrate is not distributed through the parts. Thus I am enabled to provide mold parts of greater strength and in less time than heretofore.

The benecial effect of ammonium nitrate dis-y tributed through a mold part that is to be baked is evidenced not only by improved strength and reduced baking time, shown by actual test, but also by the color of the baked part. Core makers generally depend upon the color 0f baked cores as an indication of proper baking. That is, as baking progresses the colorof the core deepens until it reaches a relatively dark brown shade, and the ordinary belief is that cores of lighter shade have been baked insuiliciently. Many tests have shown that the desired shade is attained much more quickly in the practice of this invention than with sand mixes of like composition but not containing ammonium nitrate. Many tests have shown also that the interior of the mold part attains the desired shade more rapidly. Moreover, at that shade mold parts made in accordance with the invention possess greater strength than similar parts made in the same way but without using ammonium nitrate, thus showing that the attainment of proper color in the practice of the invention may be used as a reliable guide. In ordinary practice, i; e., as followed priorto this invention, the oxidation of the oil proceeds'from the surface of the mold part toward the center. Often the surface of the core or other mold part attains the nished color long before the interior is fully baked. The

'use of ammonium nitrate in accordance with thisv mullers, for example by mixing the ammonium- ,nitrate and sand prior to or after the addition of the oil binder. Or, and preferably, a solution of ammonium nitrate in water is used in place of part or all of the w'ater that is used for temperlng the mixture to render it sufciently form-4 able for shaping, the solution being of such con- 2 per cent of linseed oil which was tempered with `5` per cent of water, based on the weight of the mix. This gave a permeability of 20. The briquettes were baked at 425 F. Again, similar results were obtained with a mix intermediate the neness of the two foregoing mixtures and composed of 99 per centof sand of 80 flneness and 1 part of raw linseed oil. tempered with 2 .per cent of moisture.

In all cases the tensile strength briquettes attained the desired color, which is one of the tests relied on by core makers to determine the coml pletion of baking, in much less time than in the centration and used in an amount such as to supply the proper amount of ammonium nitrate.

In accordance with the invention there should be added at least about 0.1 per cent of ammonium nitrate based on the weight of the mixture, and not more than about 2, or at most 3, per cent. Experience has shown that optimum results'are usually obtained at about 0.3 per cent, which I prefer for that reason and because that amount affords greater economy than Where the upper limit stated is approached.

The results obtainable through the invention are exemplified by the data given inthe accompanying drawing. Briquettes for the standard tensile strength test set up by the American Foundrymens Association were made from a mix comprising, by weight, 98 per cent of sand (42 iineness) and 1 per cent each.of linseed oil and cereal ilour. This was tempered with 2.6 per cent by weight of moisture, based on the foregoing composition. A series of briquettes were made from that mixture, and similar briquettes were made from the mixture to which there were added varying amounts of ammonium nitrate, as indicated with relation to the various curves. The briquettes were then baked at 380 F., and they were withdrawn after various intervals of time, beginning with 30 minutes baking, and their strengths determined.

The curves show that using 0.3 per cent of ammonium nitrate the tensile strength of the briquettes after BO-mlnutes baking was increased 37 p.s. i. in comparison with those containing no ammonium nitrate, representing a 32 per cent increase, while with 1 per cent of ammonium nitrate the increase in strength was almost 48 per cent. The maximum strength obtained without ammonium nitrate was developed after baking 1 hour, and the curves show that all of the briquettes containing ammonium nitrate were substantially stronger after that length of baking than the briquettes Without ammonium nitrate. The curves show also that the best strengths for all time intervals after 45 minutes were obtained with theaddition of 0.3 per cent of the nitrate. Generally similar results have been obtained with other types of mixes, indicating in each case the attainment of the best results at about 0.3 per cent of ammonium nitrate. My tests have shown also that in general the greater the amount of ammonium nitrate the less will be the strength as compared with 0.3 per cent.

The mix represented by Fig. l, as described above, had a permeability of 2'80 according to the American Foundrymens Association specification. Work With other compositions has shown that the invention is equally applicable to them and with generally similar results. For instance, the optimum concentration of 0.3 per cent of ammonium nitrate has been demonstrated also with a mixture of 68 per cent of sand (42 flneness) 32 per cent of silica flour and case of the briquettes without ammonium nitrate. Of course, the ammonium nitrate is substantially wholly decomposed at the temperatures used in the mold baking, and the results that characterize the invention are due to the action of the decomposition products.

According to the provisions of the patent statutes, I have explained the principle and mode of practicing my invention and have described what I now consider to represent its best embodi-v ment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1. In4 a method of making oil bonded sand mold parts, the step comprising incorporating in the unbaked part from about 0.1 to 3 'per cent by weight of ammonium nitrate. and then baking the part with decomposition of said ammonium nitrate.

2. In a method of making oil bonded sand mold parts, the step comprising incorporating throughout the unbaked part from' about 0.1 to 2 per cent by weight of ammonium nitrate, and then baking the part with decomposition of said ammonium nitrate and thereby reducing the baking time and conferring increased strength and effecting more uniform baking throughout as compared with a similar part without said ammonium nitrate.

3. In a method of making oil bonded sand mold parts, the f step comprising incorporating throughout the baked part about 0.3 percent by Weight of ammonium nitrate, and then baking the part with decomposition of said ammonium nitrate and thereby reducing the baking time and conferring increased strength and eiecting more uniform baking throughout as compared with a similar part without said ammonium nitrate.

4. That method of making oil bonded sand mold parts comprising the steps of mixing foundry sand, core oil and an aqueous solution of ammonium nitrate in an amount to provide from about 0.1 to 3 per cent by weight of ammonium nitrate, forming the parts from the batch, and then baking said parts, with decomposition of said ammonium nitrate.

5. That method of making oil bonded sand mold parts comprising the steps of mixing foundry sand, core oil and an aqueous solution of ammonium nitrate to produce a formable batch, said solution providing about 0.3 per cent by weight of ammonium nitrate,'forming the parts from said batch, and then baking said parts with decomposition of said ammonium nitrate and thereby producing baked parts of increased strength and more uniformly baked throughout in less time as compared with similar parts without said ammonium nitrate.

DAY E. CUTLER. (References on following page) REFERENCES CITED Number Name Date The following references are of record in the z'ggg l pr'z' 111e of this patent: ee e e a' ug' 2,137,715 Erdmann etal Nov. 22, 1938 UNITED STATES PATENTS Number OTHER REFERENCES Name Date Trans. American Foundrymans Assoc., vol. Knapper Dec. 17, 1918 XXUV, pages 590-591 (1926), vol. XXXVII, Hemelius July 1, 1919 page 294. Sampson July 12,1932 10 Hackhs- Chem. Dictionary, 3d ed., page 48 Weidemann Nov. 22, 1932 4(1944) Malaspina 001;.2, 1934 Moldenke, Principles of Iron Founding," 2d Wallace et al Sept, 24, 1940 ed., page 375 (1930). 

